code: def test_training_on_cpu_only_env(self):
      cuda_environment = {"CUDA_VISIBLE_DEVICES": "-1"}
      env = os.environ.copy()
      env.update(cuda_environment)
      args = self.args_template.copy()
      args.append(
          "./tests/python-gpu/"
          "load_pickle.py::TestLoadPickle::test_training_on_cpu_only_env"
      )
      status = subprocess.call(args, env=env)
      assert status == 0
  
file_path: xgboost/tests/python-gpu/test_gpu_pickling.py
imports: import os
  import pickle
  import subprocess
  import numpy
  import pytest
  import xgboost
  from xgboost import XGBClassifier
  from xgboost import testing
label_desc: Use image node_id 6 for calling the TestPickling obj's underlying member method code with example usage: obj.test_training_on_cpu_only_env() without return types